Toxic, airborne contaminants, such as carbon monoxide, mercury, ethylene oxide, volatile organic materials and hydrogen sulfide, are often difficult to detect, since they may be colorless and odorless or they may be toxic at levels below which they can be seen or smelled by an average person. Also, in many environments, the smell of these gases may be masked by other odors that are present in the air. However, these airborne toxins present a growing danger to humans in, for example, automobiles, airplanes, industrial plants, mines, homes, and other environments in which humans are present for extended periods of time.
Numerous chemical detector tubes, for detecting the presence of toxins, have been in use for many years. For example, the use of palladium and molybdenum salts for carbon monoxide detection is described in Analytical Chemistry, Vol. 19, No. 2, pages 77-81 (1974). K. Shuler and G. Schrauzer improved upon this technology by adding a third metallic salt component which produces a self-regenerating catalyst that is short-lived. This catalyst, disclosed in U.S. Pat. No. 4,043,934, uses the impregnation of a carbon monoxide-sensitive chemical catalyst solution into powdered silica-gel substrates to give detectors sensitive-to-low concentrations of atmospheric carbon monoxide. While this system is effective in detecting carbon monoxide, it has not met with commercial acceptance due to the short functional life of the catalyst.
It is generally recognized that, for a carbon-monoxide sensor system to be commercially useful, it must have a functional life of at least one year. Tests have shown that the material described in U. S. Pat. No. 4,043,934 has a working life of only two to four months at room temperature and only three to four days at forty degrees Celsius.
Therefore, there is a need for a chemical sensor system capable of detecting the presence of airborne toxins, such as carbon monoxide, mercury, ethylene oxide, volatile organic materials and hydrogen sulfide, which has a functional life of at least one year. In addition, since these chemical sensor systems are designed to prevent injury to humans, it is important that the sensitivity of these sensor systems be similar to that of humans.